The TLC study is a multi-center, randomized, placebo-controlled, double-blind clinical trial of lead chelation with the drug succimer for children 12-33 months of age with baseline blood lead concentrations between 20 and 44 ug/dl. The primary outcome of interest is developmental status as measured by full-scale devation IQ score using the Wechsler Preschool and Primary Scales of Intelligence three years after randomization. Secondary objectives include the evaluation of the effects of lead chelation on other measures of developmental status, particularly tests of neuro-psychological developmental (including attention and executive function); changes in height, weight and head circumference, and changes in systolic and diastolic blood pressure levels. In addition, the interactions between iron deficiency and low moderate level lead poisoning are being explored. The study involves 1:1 randomization of children at four clinical centers in Philadelphia, Newark, Cincinnati, and Baltimore. Both treatment assignments and lead laboratory measures are double-blinded. Enrollment at the CHOP site was completed on January 17, 1997. A total of 165 children were randomized at this site. To achieve this enrollment, approximately 500 children were screened for the study. To date, 60 children have completed the study, 99 remain in follow-up and 6 are lost to follow-up. Final assessments will be completed by January, 2000.